Semiconductor light emitting device, image display system and illumination device

ABSTRACT

Disclosed are a semiconductor light emitting device capable of enhancing a light emergence efficiency at a lower light emergence plane of the device by forming an electrode on a halfway area of a tilt crystal plane and a fabrication method thereof. According to this light emitting device, since light emitted by a light emitting region can be efficiently, totally reflected and a current can be injected only in a good crystalline region for the reason that the halfway area, on which the electrode is formed, of the tilt crystal plane is better in crystallinity than other regions of the tilt crystal plane, it is possible to enhance both a light emergence efficiency and a luminous efficiency, and hence to enhance the light emergence efficiency by an input current. According to an image display system and an illuminating system, each of which includes an array of the semiconductor light emitting devices of the present invention, and fabrication methods thereof, since the light emitting devices each of which is capable of exhibiting a high luminous efficiency by an input current are arrayed on a substrate on the system, it is possible to provide an image display system capable of reducing a density of a current to each device and displaying a high quality image, and an illuminating system capable of ensuring high brightness.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 10/450,096,filed on Sep. 25, 2003, now U.S. Pat. No. 6,963,086 entitledSEMICONDUCTOR LIGHT EMITTING DEVICE, IMAGE DISPLAY SYSTEM ANDILLUMINATING DEVICE, AND FABRICATION METHODS THEREOF which, in turn,claims priority to International application No. PCT/JP02/09898, filedSep. 25, 2002, which, in turn, claims priority to Japanese applicationNo. JP2001-312207, filed Oct. 10, 2001.

TECHNICAL FIELD

The present invention relates to a semiconductor light emitting devicehaving a double-hetero structure that crystal layers composed of a firstconductive type layer, an active layer, and a second conductive typelayer are formed on a crystal growth layer, wherein the crystal layershave tilt crystal planes tilted from the principal plane of a substrate.In particular, the present invention relates to a semiconductor lightemitting device having a high light luminous efficiency and afabrication method thereof, and an image display system and anilluminating system, each of which includes an array of thesemiconductor light emitting devices, and fabrication methods thereof.

BACKGROUND ART

Semiconductor light emitting devices have been known, which arefabricated by stacking, on the entire surface of a sapphire substrate,an n-side contact layer made from GaN doped with Si, an n-side claddinglayer made from GaN doped with Si, an active layer made from InGaN dopedwith Si, a p-side cladding layer made from AlGaN doped with Mg, and ap-side contact layer made from GaN doped with Mg. These devices havingsuch a structure have been commercially available as industrialized blueand green LEDs (Light Emitting Diodes) for emission of light in a rangeof 450 nm to 530 nm.

Various methods have been proposed to increase brightness ofsemiconductor light emitting devices. These methods are mainlyclassified into a method of improving a luminous efficiency on the basisof a current inputted in the device and a method of improving a lightemergence efficiency by allowing emitted light to efficiently emerge outof the device. The former improvement of the luminous efficiency isdependent on a material forming a crystal layer, a crystal structure, acrystal growing ability, a combination of crystal layers, and afabrication process. With respect to the latter improvement of the lightemergence efficiency, it is required to examine reflection of lightdepending on a device structure and an array structure of the devicesmounted on a system device, and it is important to allow emitted lightto emerge out of the device without damping and leakage.

With respect to the method of improving the light emergence efficiencyon the basis of an input current, particularly, in a device having atilt crystal plane tilted from the principal plane of a substrate, alight emitting region composed of a first conductive type layer, anactive layer, and a second conductive type layer can be formed on thewhole or part of the S-plane. In the case where the device is formedinto an approximately hexagonal truncated shape, a first conductive typelayer, an active layer, and a second conductive type layer can be formedeven on the upper surface parallel to the principal plane of asubstrate. In the case of a semiconductor light emitting device formedinto a flat shape having a plane parallel to the principal plane of asubstrate, light is damped by multi-reflection. On the contrary, in thecase of the semiconductor light emitting device having the S-plane,since light emission is performed by making use of the S-plane, light isallowed to emerge out of the device from the light emergence planewithout the effect of multi-reflection. The crystal layer having theS-plane may be configured such that part of the crystal plane formingthe S-plane function as the first conductive type layer. Further, thecrystal layer having a crystal plane not perpendicular to the principalplane of a substrate is effective to improve the light emergenceefficiency.

In a semiconductor light emitting device having a tilt crystal plane,the luminous efficiency can be enhanced by making use of goodcrystallinity of the tilt crystal plane. In particular, in the case ofinjecting a current only in the S-plane having good crystallinity, sincethe S-plane exhibits good incorporation of In and good crystallinity,the luminous efficiency can be enhanced. In addition, the area of theactive layer extending within a plane substantially parallel to theS-plane can be made larger than the area of the active layer projectedon a substrate or the principal plane of an underlying growth layer.With this configuration, since the area of the light emission areabecomes substantially large, it is possible to reduce a current density,and to reduce saturated brightness and hence to increase the luminousefficiency.

By the way, in the above-described semiconductor light emitting devicehaving the tilt crystal plane tilted from the principal plane of asubstrate, if the device has a hexagonal pyramid shaped crystal layer,the state of steps of a portion, neat the vertex, of the S-plane becomespoor, with a result that the luminous efficiency of the vertex portionis degraded. The reason for this is as follows: namely, assuming that aplane of the hexagonal pyramid shape is divided into a vertex side area,a left side area, a right side area, and a bottom side area by two linespassing through with respect to an approximately center portion of theplane, the state of steps on the vertex side area is particularly wavy,with a result that abnormal growth of crystal is liable to occur in thevertex side area. On the contrary, in each of the right and left sideareas, steps densely extend in the forms of approximately straightlines, with a result that crystal is very desirably grown, and in thebottom side area, steps are slightly wavy, with a result that thecrystal growth state is poorer than that in each of the right and leftside areas.

If a p-side electrode is formed in a region, in which the state of stepsis undesirable, of the tilt crystal plane, the luminous efficiency onthe basis of an input current becomes lower than that of the case wherethe p-side electrode is formed in a region in which the state of stepsis desirable. Accordingly, it is desirable to form an electrode in aregion other than an area in the vicinity of the vertex portion in whichthe state of steps is wavy and an area in the vicinity of the bottomsurface in which the state of steps is slightly wavy.

On the other hand, in the case of forming an electrode on a tilt crystalplane, since the electrode is tilted relative to a light emergence planeof the device, it is possible to suppress multi-reflection of emittedlight and hence to suppress damping of light, and to allow lightreflected from the electrode to emerge out of the light emergence planeprovided on the bottom surface of the device.

However, if an electrode is not formed in the areas, in the vicinitiesof the vertex and the bottom surface of the device, of the tilt crystalplane, the ratio of a light component not reflected from the electrodein the light emergence direction to light emitted by a light emittingregion becomes high.

Further, of the light reflected from the electrode formed on the tiltcrystal plane, a light component having a large incident angle relativeto the light emergence plane is totally reflected from the lightemergence plane and thereby is not allowed to emerge out of the device.As a result, even if an electrode is formed only in a good crystallineregion to improve the luminous efficiency, it is impossible to enhancethe light emergence efficiency and hence to sufficiently obtain theeffect of forming the light emitting region only in a good crystallinearea.

In view of the foregoing, the present invention has been made, and anobject of the present invention is to provide a semiconductor lightemitting device capable of enhancing the luminous efficiency whileincreasing the light emergence efficiency, and a fabrication methodthereof, and to provide an image display system and an illuminatingsystem, each of which includes an array of the semiconductor lightemitting devices, and fabrication methods thereof.

DISCLOSURE OF INVENTION

According to a semiconductor light emitting device in which an electrodeis formed in a halfway area of a tilt crystal plane and a fabricationmethod thereof according to the present invention, the electrode formedin the halfway area of the tilt crystal plane is located at such aposition as to allow light emitted from a crystal layer to which acurrent is injected by the electrode to be efficiently, totallyreflected from the surface of a portion, provided with no electrode, ofthe tilt crystal plane. As a result, it is possible to enhance the lightemergence efficiency from a light emergence plane on the lower side ofthe device. Further, since the emitted light can be efficiently, totallyreflected as described above and the halfway area, on which theelectrode is formed, of the tilt crystal plane is better incrystallinity than other regions of the tilt crystal plane, it ispossible to inject a current only in the good crystalline region, andhence to enhance the luminous efficiency. By enhancing both the lightemergence efficiency and the luminous efficiency, it is possible to forma semiconductor light emitting device exhibiting a high emergenceefficiency on the basis of an input current.

According to an image display system and an illuminating system, each ofwhich includes an array of semiconductor light emitting devicesaccording to the present invention, since light emitting devices each ofwhich exhibits a high light emergence efficiency on the basis of aninput current are arrayed on a system substrate, it is possible toprovide an image display device capable of reducing the density of acurrent to each device and displaying a high quality image, and toprovide an illuminating system capable of ensuring high brightness. Inparticular, the image display system and illuminating system, each ofwhich includes the array of a large number of light emitting devices,have a large effect of reducing power consumption.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view schematically showing the structureof a semiconductor light emitting device according to an embodiment ofthe present invention;

FIG. 2 is a sectional view showing an electrode structure of asemiconductor light emitting device according to a first embodiment ofthe present invention;

FIG. 3 is a partial sectional view showing the electrode structure ofthe semiconductor light emitting device according to the firstembodiment of the present invention;

FIG. 4 is a sectional view showing an electrode structure of asemiconductor light emitting device according to a second embodiment ofthe present invention;

FIG. 5 is a partial sectional view showing an electrode structure of asemiconductor light emitting device according to a third embodiment ofthe present invention;

FIGS. 6A and 6B are a sectional view and a plan view showing thestructure of a semiconductor light emitting device in a process offabricating an image display system according to a fourth embodiment ofthe present invention, respectively;

FIG. 7 is a sectional view showing a device transfer step in the processof fabricating the image display system according to the fourthembodiment of the present invention;

FIG. 8 is a sectional view of a device holding state after transfer ofdevices in the process of fabricating the image display system accordingto the fourth embodiment of the present invention;

FIG. 9 is a sectional view showing a resin-molded device forming step inthe process of fabricating the image display system according to thefourth embodiment of the present invention;

FIG. 10 is a sectional view showing a step of aligning a resin-moldeddevice to an attracting hole in the process of fabricating the imagedisplay system according to the fourth embodiment of the presentinvention;

FIG. 11 is a sectional view showing a step of fixing a resin-moldeddevice to a system substrate in the process of fabricating the imagedisplay system according to the fourth embodiment of the presentinvention;

FIG. 12 is a sectional view showing a step of arraying resin-moldeddevices on the system substrate in the process of fabricating the imagedisplay system according to the fourth embodiment of the presentinvention; and

FIG. 13 is a sectional view showing a wiring formation step in theprocess of fabricating the image display system according to the fourthembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In this embodiment, the structure of a tilt crystal layer tilted fromthe principal plane of a substrate according to the present inventionwill be described, and then a formation position of an electrode to beformed on a tilt crystal plane will be described. After that, anelectrode structure will be described, and then an image display systemand an illuminating system, each of which includes semiconductor lightemitting devices each having an electrode formed in a halfway area ofthe tilt crystal plane according to the present invention andfabrication methods thereof, will be descried.

A substrate used for growing a crystal layer according to the presentinvention may be made from any material without departing from the scopeof the present invention. In particular, in the case of forming acrystal layer having a tilt crystal plane tiled from the principal planeof a substrate, the substrate may be made from a material selected fromsapphire (Al₂O₃, containing the A-plane, R-plane, and C-plane), SiC(containing 6H, 4H, and 3C), GaN, Si, ZnS, ZnO, AlN, LiMgO, GaAs,MgAl₂O₄, InAlGaN, and the like. Preferably, the above material has ahexagonal crystal system or a cubic system, and more preferably, it hasthe hexaganal system. For example, in the case of using a sapphiresubstrate, the C-plane of sapphire, which has been often used forgrowing gallium nitride (GaN) based compound semiconductors, is used asthe principal plane of the substrate. The C-plane used herein maycontain a plane tilted from the strict C-plane by an angle of 5 to 6°.The substrate is not contained in a light emitting device as a product.That is to say, the substrate is used for holding a device portionduring fabrication process, and is removed before the device isaccomplished. The material of the substrate is not limited to sapphirebut may be a material having light permeability, such as galliumnitride, glass, or a transparent resin. A substrate on which a device isto be formed by crystal growth may be separated from a substrate towhich the device is to be mounted by transfer or the like.

Before a tilt crystal layer tilted from the principal plane of asubstrate is formed, an underlying growth layer may be formed on thesubstrate. The underlying growth layer may be made from gallium nitrideor aluminum nitride. Alternatively, the underlying growth layer may be acombination of a low temperature crystal growth layer and a hightemperature crystal growth layer or a combination of a crystal growthlayer and a crystal seed layer functioning as a crystal seed.

The crystal layer having a tilt crystal plane tilted from the principalplane of a substrate is not particularly limited insofar as a lightemitting region composed of a first conductive type layer, an activelayer, and a second conductive type layer can be formed thereon.Preferably, the crystal layer has a wurtzite crystal structure. Examplesof the material suitable for the crystal layer include a group III basedcompound semiconductor, a BeMgZnCdS based compound semiconductor, andBeMgZnCdO based compound semiconductor, and further, an indium nitride(InN) based compound semiconductor, an indium gallium nitride (InGaN)based compound semiconductor, and aluminum gallium nitride (AlGaN) basedcompound semiconductor. In particular, a nitride semiconductor such as agallium nitride based compound semiconductor is preferably used as thematerial for the crystal layer. A tilt crystal plane of the crystallayer contains a plane tilted from the S-plane or the (11-22) plane byan angle of 5 to 6°.

The first conductive type layer is a p-type or n-type cladding layer,and the second conductive type layer is the opposed conductive typecladding layer. In the case where the crystal layer having the S-planeis made from a silicon-doped gallium nitride based compoundsemiconductor layer, a silicon-doped gallium nitride based compoundsemiconductor layer may be formed as the n-type cladding layer, an InGaNlayer be formed thereon as the active layer, and a magnesium-dopedgallium nitride based compound semiconductor layer be formed thereon asthe p-type cladding layer, to form a double-hetero structure. The activelayer may have a structure that the InGaN layer is sandwiched betweenAlGaN layers. The active layer can be formed as a single bulk activelayer, but may be formed as a quantum well structure such as a singlequantum well (SQW) structure, a double quantum well (DQW), or amulti-quantum well (MQW) structure. The quantum well structure mayinclude a barrier layer for separating quantum wells as needed. Theactive layer made from InGaN is advantageous in easy fabrication andimprovement of light emitting characteristics of the device. Further, inthe case of forming the InGaN layer on the S-plane from which nitrogenatoms are less desorbed, the InGaN layer is easy to grow on the S-plane,and is capable of improving the crystallinity, thereby enhancing theluminous efficiency.

In the case of selective crystal growth, if any crystal seed layer isnot provided, the crystal layer must be formed from the crystal growthlayer, and if the crystal layer is formed from the crystal growth layerby selective growth, crystal tends to grow on a portion at which thecrystal growth is inhibited. For this reason, the crystal seed layer maybe used for growth of crystal with good selectivity.

The selective growth method will be concretely described below. Theselective growth is performed by making use of selective removal of partof an underlying growth layer, or making use of an opening portionselectively formed on an underlying growth layer or before formation ofthe underlying growth layer. For example, if the underlying growth layeris composed of a crystal growth layer and a crystal seed layer, thecrystal seed layer on the crystal growth layer may be divided into fineregions each having a diameter of about 10 μm, and then a crystal layerhaving the S-plane or the like may be formed by crystal growth from thefine regions. For example, the fine regions divided from the crystalseed layer may be arrayed so as to be spaced from each other atintervals as margins for separating a device structure into individuallight emitting devices. Such a fine region may be formed into a shapeselected from a circular shape, a square shape, a hexagonal shape, atriangular shape, a rectangular shape, a diamond-like shape, and othershapes modified therefrom. The selective growth can be performed byforming a mask layer on the underlying growth layer, and selectivelyforming an opening as a window region in the mask layer. The mask layermay be made from silicon oxide or silicon nitride. In the case offorming the crystal layer having an approximately hexagonal truncatedpyramid or approximately hexagonal pyramid shape extending in straightline along the longitudinal direction, a stripe shaped window region maybe formed in the mask layer.

In the case of selectively growing the crystal layer only over anopening portion formed in a selective growth mask, since there is nolateral growth, crystal may be laterally grown into a shape enlargedfrom the opening portion (the window region) by a micro-channel epitaxyprocess. It is known that the lateral growth by using the micro-channelepitaxy process is advantageous in avoiding threading dislocations,thereby reducing the density of the dislocations. The lateral growth isalso advantageous in enlarging a light emitting region, equalizing acurrent, avoiding the concentration of a current, and reducing a currentdensity.

The crystal layer having a tilt crystal plane tilted from the principalplane of a substrate may be formed into an approximately hexagonalpyramid shape having, on the tilt planes, the S-planes or planessubstantially equivalent thereto, or formed into an approximatelyhexagonal truncated pyramid shape having, on the tilt planes, theS-planes or planes substantially equivalent thereto and also having, onthe upper end portion, the C-plane or a plane substantially equivalentthereto. Such an approximately hexagonal pyramid or approximatelyhexagonal truncated pyramid shape is not limited to the strict hexagonalpyramid or hexagonal truncated pyramid shape, but may miss one or moreplanes thereof. As a preferable example, the crystal layer has tiltcrystal planes which are approximately symmetrically disposed. Theapproximately symmetrical shape contains the perfectly symmetrical shapeand a shape somewhat offset from the perfect symmetrical shape. Theridge line between adjacent two of crystal planes of the crystal layeris not necessarily a straight line. Further, the above-describedapproximately hexagonal pyramid or approximately hexagonal truncatedpyramid shape may extend in straight line.

These first conductive type layer, the active layer, and the secondconductive type layer extend within planes parallel to the tilt crystalplanes tilted from the principal plane of a substrate. The formation ofthese layers such that they extend the planes parallel to the principalplane of the substrate may be easily realized by continuing crystalgrowth for these layers immediately after the formation of the tiltcrystal planes. In the case of forming the crystal layer having anapproximately hexagonal pyramid or approximately hexagonal truncatedpyramid shape which has the S-planes as the tilt crystal planes, thelight emitting region composed of the first conductive type layer, theactive layer, and the second conductive type layer can be formed on thewhole of part of the S-planes. In the case of an approximately hexagonaltruncated pyramid shape, the first conductive type layer, the activelayer, and the second conductive type layer can be formed even on theupper plane parallel to the principal plane of a substrate. In the caseof the crystal layer having a flat shape parallel to the principal planeof a substrate, light is damped by multi-reflection. On the contrary,the crystal layer configured such that light emission is performed byusing the tilt S-planes is advantageous in that light merges out of thesemiconductor device without any effect of multi-reflection because ofthe presence of the tilt planes. Accordingly, the crystal layer havingcrystal planes not perpendicular to a substrate is able to improve thelight emergence efficiency. The first conductive type layer, that is,the cladding layer can be made from the same material as that of thecrystal layer having the S-planes so as to have the same conductive typeas that of the crystal layer, and therefore, it can be easily formed byadjusting, after formation of the crystal layer having the S-planes, theconcentration of the source gas. Alternatively, part of the crystallayer having the S-plane may be made to function as the first conductivetype layer.

In the above-described semiconductor light emitting device, the luminousefficiency can be enhanced by making use of good crystallinity of thetilt crystal planes. In particular, in the case of injecting a currentonly in the S-plane having good crystallinity, since the S-planeexhibits good incorporation of In and good crystallinity, the luminousefficiency can be enhanced. In addition, the area of the active layerextending within a plane substantially parallel to the S-plane can bemade larger than the area of the active layer projected on a substrateor the principal plane of an underlying growth layer. With thisconfiguration, since the light emission area becomes large, it ispossible to reduce a current density, and to reduce saturated brightnessand hence to increase the luminous efficiency.

According to the present invention, it is intended to provide anelectrode forming a light emitting region in a good crystalline area ofan approximately hexagonal pyramid shape formed by selective growth, andto efficiently reflect light emitted by the light emitting region fromthe electrode and a portion, provided with no electrode, of the tiltcrystal plane and lead the reflected light to a light emergence plane.The formation position of such an electrode will be first described.

FIG. 1 is a schematic sectional view showing the structure of anapproximately hexagonal pyramid shaped semiconductor light emittingdevice formed by selective growth from an opening portion (not shown)formed in a crystal growth substrate. A point A is the vertex of thedevice, and FIG. 1 shows the cross-sectional view of the device taken ona plane which is perpendicular to the bottom surface of the device andwhich contains the point A. The device is fabricated by forming acrystal growth layer 1 on the substrate and a tilt crystal layer 2 onthe crystal growth layer 1. The tilt crystal layer 2 has a multi-layerstructure of a first conductive type layer having tilt crystal planestilted from the principal plane of the substrate, an active layer formedon the tilt crystal layer, and a second conductive type layer formed onthe active layer, wherein electrodes 3 a and 3 b are formed on halfwayareas of the second conductive type layer. Light emitted from a lightemitting region of the active layer emerges out of the device. At thistime, the bottom surface of the hexagonal pyramid shaped semiconductorlight emitting device is taken as a light emergence surface. It is to benoted that the multi-layer structure of the second conductive typelayer, the active layer, and the second conductive type layer is notshown in the figure. In the figure, there are shown the crystal growthlayer 1 for growing the tilt crystal layer, a bottom side BC containedin the bottom surface, light emitting regions 4 a and 4 b, the outermosttilt crystal planes, and the electrodes 3 a and 3 b formed on thehalfway areas of the outermost tilt crystal planes. The light emittingregions 4 a and 4 b are defined as regions, on which the electrodes 3 aand 3 b are projected, of the active layer extending in parallel to thetilt crystal planes. A current is substantially injected from theelectrodes 3 a and 3 b in the light emitting regions 4 a and 4 b.

The formation positions of the electrodes 3 a and 3 b will be describedwith reference to FIG. 1. First, bottom ends of the bottom side of theapproximately hexagonal pyramid portion of the device are taken aspoints B and C, and the vertex of the device is taken as a point A. Thetilt crystal layer is grown in the height direction while beingsymmetrically spread in the lateral direction from the center of theside BC contained in the growth initiating plane of the tilt crystallayer. The lengths of the side AB and the side AC are nearly equal toeach other, and the angle ABC and the angle ACB are equal to each other.Accordingly, the triangle ABC is an isosceles triangle having the anglesABC and ACB equal to each other. The angle ABC is here defined as θ. Itis to be noted that the crystal growth layer 1 is formed on thesubstrate (not shown), and is made from the same material as that of thetilt crystal layer 2, which material is a GaN based material in thisembodiment.

The side AB is extended from the point B, and an intersection at whichthe extended straight line from the side AB intersects the back surfaceof the crystal growth layer 1 is taken as a point P. An intersection atwhich a straight line extending in perpendicular to the front surface ofthe crystal growth layer 1 while passing through the point B intersectsthe back surface of the crystal growth layer 1 is taken as a point Q.The lower end of an electrode formed on the tilt crystal planecontaining the side AC is taken as a point D. An intersection at which astraight line extending from the point D in the direction parallel tothe side BC intersects the side AB is taken as a point E. Anintersection at which a straight line extending from the point E in thedirection parallel to the side BD intersects the side AC is taken as apoint R. Based on these points thus defined, the electrode 3 a havingboth ends located at the points D and F is formed on the tilt crystalplane containing the side AC, and similarly the electrode 3 b havingboth the ends located at the points E and G is formed on the tiltcrystal plane containing the side AB.

To achieve efficient emergence of light out of the device, it isrequired to enhance both the light emergence efficiency and the luminousefficiency of the device. That is to say, it is required to form anelectrode on the tilt crystal plane at such a position as to obtain mostefficient emergence of light out of the device from the viewpoints ofboth the above-described efficiencies. The conditions for enhancing boththe light emergence efficiency and the luminous efficiency will bedescribed below.

First, the condition for enhancing the light emergence efficiency in thecase of forming an electrode on a halfway area of the tilt crystal planewill be described. To enhance the light emergence efficiency, it isrequired to reflect light emitted by the light emitting region from theelectrode and the boundary between the tilt crystal plane and theoutside and lead the light to the light emergence plane. FIG. 1typically shows the device such that the outermost tilt crystal planeson which the electrodes 3 a and 3 b are formed correspond to thesubstantial light emitting regions 4 a and 4 b of the active layer.Hereinafter, description will be made by example of a light component,made directly incident on the light emergence plane, of light emittedfrom the light emitting region 4 a (which light component is hereinafterreferred to as “directly incident light component”), and a lightcomponent, reflected once from the electrode or the tilt crystal planeand made incident on the light emergence plane, of multi-reflected light(which light component is hereinafter referred to as “indirectlyincident light component”).

The directly incident light component directly travels from the lightemitting region 4 a of the active layer to the side BC, and is therebynot reflected from the electrode or the tilt crystal plane. In thisembodiment, since the light emitting region 4 a is tilted from the sideBC, the area of the light emitting region can be made substantiallylarger than that of a light emitting region extending in parallel to theside BC, with a result that a larger amount of light is able to emergeout of the device.

First, of light emitted by the light emitting region 4 a, a lightcomponent traveling to a portion of the tilt crystal plane, whichportion is located on the side EB of the side AB opposed to the side AC,will be described. Since any electrode is not formed on the side EB, thelight component, traveling to the side EB, of the light emitted by thelight emitting region 4 a is not reflected from the electrode. As aresult, it is desirable that the light emitted by the light emittingregion 4 a is totally reflected from the portion, provided with noelectrode, of the tilt crystal plane with little passing there through.At this time, of the light component, traveling to the side EB, of thelight emitted by the light emitting region 4 a, a light component parttraveling to the point B at the largest angle relative to the side EB isthat emitted from the vicinity of the point D of the light emittingregion 4 a at an angle DBE relative to the side EB. As a result, if theangle DBE of light emitted from the vicinity of the point D is acritical angle of light totally reflected from the side EB, the lightcomponent, traveling to the point B, of the light emitted by the lightemitting region 4 a is totally reflected from the point B.

By the way, according to this embodiment, the nearly whole portion ofthe crystal layer having the triangular shape ABC is substantially madefrom the same GaN based material as that of the crystal growth layer 1,and accordingly, the optical characteristics, such as a refractiveindex, of the crystal layer having the triangular shape ABC are nearlyequal to those of the crystal growth layer 1. As a result, the lightcomponent traveling at the angle DBE relative to the side EB andentering the point B is totally reflected from the point B at an angleQBP relative to the side BP. Here, if light is totally reflected fromthe point B, the incident angle DBE of the light is equal to areflection angle QBP (∠DBE=∠QBP) of the light. On the other hand, thevertical angle of the incident light is equal to that of the reflectionlight. Accordingly, a relationship of ∠QBP=90°−θ is established. As aresult, with respect to light emitted by the light emitting region 4 aand totally reflected from the point B, a relationship of∠DBE=∠QBP=90°−θ is established. Therefore, an angle DBC, whichdetermines the position of the point D, that is, the lower end of theelectrode 3 a, is specified by a relationship of∠DBC=∠ABC−∠DBE=θ−(90°−θ)=2θ−90°.

Next, the condition under which a light component emitted from thevicinity of the point F, that is, the upper end of the electrode 3 a inthe light emitting region 4 a is totally reflected from the side EB willbe described. Of the light component emitted from the vicinity of thepoint F in the light emitting region 4 a and traveling to the side EB, alight component part made incident on the side EB at the largestincident angle is that traveling to the point E. Accordingly, if anangle FEA is a critical angle of total reflection, the light componentemitted from the vicinity of the point F in the light emitting region 4a and traveling to the side EB is totally reflected from the side EB, totravel to the light emergence plane. By the way, the side FE is parallelto the side DB and the angle DBE is the critical angle of light totallyreflected from the portion, located on the side AB, of the tilt crystalplane, the angle DBE is equal to an angle FEG (∠DBE=∠FEG). As a result,the light component, traveling to the point E, of the light emitted fromthe vicinity of the point F in the light emitting region 4 a is totallyreflected from the point E, and is therefore, totally reflected from allthe points on the side EB.

By setting both the ends of the electrode 3 a at the points D and F, alight component, traveling to the side EB, of light emitted from thevicinity of each end of the light emitting region 4 a is effectively,totally reflected from the side EB. Most of a light component, travelingto the side EB, of light emitted from a portion between both the ends ofthe light emitting region 4 a is totally reflected from the side EB, totravel to the light emergence plane. A light component, traveling to theelectrode 3 b, of light emitted by the light emitting region 4 a isreflected from the electrode 3 b. To efficiently reflect light from theelectrode 3 b, it is required to examine a material capable ofsuppressing transmission of light, a film thickness, an electrodestructure, and the like, as will be described in the embodiments.

In the structure that any light reflection film is not formed in aregion containing the upper sides of the electrodes 3 a and 3 b and thevertex of the device as shown in FIG. 1, a certain proportion of lightemitted by the light emitting region is leaked out through the regioncontaining the vertex of the device, and the remaining portion of thelight is lead to the light emergence plane. Accordingly, by forming alight reflection film on the region containing the vertex portionprovided with no electrode, it is possible to suppress transmission oflight and hence to increase the light emergence efficiency. Thestructure of such a light reflection film will be described in detail inthe embodiments.

The condition required for enhancing the luminous efficiency will bedescribed below. To enhance the luminous efficiency, it is desirable toform an electrode on a portion, other than a poor crystalline region inthe vicinity of the vertex of the device and the vicinity of the bottomsurface of the device, of the tilt crystal plane. To be more specific,it is desirable that an electrode is formed on a halfway area, havinggood crystalline, of the tilt crystal plane, wherein the lower end ofthe electrode is set to a point being shifted from the upper side of thetilt crystal plane as much as possible and the upper end of theelectrode is set to a point being shifted to the lower side of the tiltcrystal plane as much as possible. This is advantageous in that lightemission can be realized by injecting a current only in a goodcrystalline region, to enhance the luminous efficiency. However, it isdifficult to clearly separate the tilt crystal plane into a goodcrystalline halfway area, in which the electrode is to be formed, and apoor crystalline area in the vicinity of the vertex of the device and inthe vicinity of the bottom surface of the device.

Part of light emitted by the light emitting region 4 a composed of theactive layer is not totally reflected from a portion, located on theside EB, of the tilt crystal plane, to pass there through. Such a lightcomponent, therefore, is not able to emerge out of the light emergenceplane. However, it is possible to realize efficient emergence of lightemitted by the light emitting region on the basis of a current inputtedin the device by combining the effect of enhancing the luminousefficiency by forming the light emitting region only in a goodcrystalline area with the effect of allowing emergence of most of lightemitted by the light emitting region from the light emergence plane.

To realize more efficient emergence of light, in addition to theconfiguration that the light emitting region is formed only in a goodcrystalline area, a current block layer having light permeability may beformed over a region containing the upper sides of the electrode and thevertex of the device and a metal thin film functioning as a lightreflection film may be formed on the current block layer. With thisconfiguration, light traveling to the vicinity of the vertex of thedevice is reflected from the reflection film toward the light emergenceplane, to emerge out of the light emergence plane. The current blocklayer formed on a poor crystalline area may be combined with a metalthin film capable of efficiently reflecting light emitted by the lightemitting region. With this configuration, it is also possible to realizeefficient emergence of light out of the light emergence plane on thebasis of a current inputted in the device.

Hereinafter, various structures of an electrode to be formed at theabove-described electrode formation position will be sequentiallydescribed, and then an image display system and an illuminating systemeach including an array of semiconductor light emitting devices eachhaving an electrode formed in a halfway area of a tilt crystal planeaccording to the present invention will be described.

It is to be noted that, for each of the following semiconductor lightemitting devices, an electrode for injecting a current in a crystallayer is formed in a halfway area of a tilt crystal plane at anelectrode position determined by the above-described angle (2θ−90°).

Embodiment 1

FIG. 2 is a sectional view showing the structure of a semiconductorlight emitting device according to a first embodiment of the presentinvention, which device is formed by crystal growth into anapproximately hexagonal pyramid shape having tilt crystal planes,wherein electrodes are formed on halfway areas of the tilt crystalplanes. As shown in the figure, electrodes 10 for efficient emergence oflight emitted by an input current to the outside of the device areformed, and a current block layer 11 is formed on the electrodes 10,upper sides from the electrodes 10, and the vertex of the device. Thehalfway areas, on which the electrodes 10 are formed, of the tiltcrystal planes have good crystallinity. The current block layer 11 isformed on the tilt crystal planes except for the vicinity of the bottomsurface, the electrodes 10, and the region in the vicinity of the vertexof the device. The current block layer 11 functions to suppressinjection of a current to the vertex portion of the crystal layer.

The structure of the electrode will be described with reference to FIG.3. A second cladding layer, which is a second conductive typesemiconductor layer 14 forming the tilt crystal planes, is a p-type GaNlayer doped with magnesium. A contact metal layer 15 having a thicknessequal to or less than a penetration depth of light emitted by an activelayer 12 formed on the crystal layer is formed on the GaN layer. Afterthe formation of the contact metal layer 15 having the specifiedthickness, an electrode layer 16 is formed on the contact metal layer15. Since the thickness of the contact metal layer 15 is equal to orless than the penetration depth of light emitted by the active layer 12,the contact metal layer can increase the reflectance of the electrodelayer 16 while ensuring good ohmic contact between the electrode layer16 and the tilt crystal planes. This is effective to increase theintensity of light reflected from the electrode layer 16 to the lighttransmission type substrate side. Since the electrode layer is formed onthe second conductive type semiconductor layer, light traveling to thesecond conductive type semiconductor layer side is reflected from theelectrode layer onto the substrate side, and since the thickness of thecontact metal layer 15 is as thin as being equal to or less than thepenetration depth of light emitted by the active layer 12, the contactmetal layer 15 can increase the reflectance of the electrode layer 16while ensuring good ohmic contact between the electrode layer 16 and thetilt crystal planes. As a result, it is possible to enhance the luminousefficiency as a whole.

The electrode structure will be more fully described below. Theelectrode 10 has a multi-layer structure formed by stacking theelectrode layer 16 on the contact metal layer 15. To be more specific,on the outermost surface of the cladding layer composed of the p-typeGaN layer as the second conductive type semiconductor layer 14, a nickellayer as the contact metal layer 15 allowing ohmic contact between thep-side electrode layer 16 and the GaN layer as the second conductivetype semiconductor layer 14 is formed as a first layer of the electrode10. The thickness of the contact metal layer 15 made from nickel is setto be equal to or less than the penetration depth of light emitted bythe active layer, and according to this embodiment, it is set to about10 nm. The p-side electrode layer 16 is formed on the contact metallayer 15 made from nickel. The p-side electrode layer 16 is representedby a thin film made from, for example, aluminum or silver. Light passingthrough the contact metal layer 15 made from nickel is reflected fromthe interface of the p-side electrode layer 16. Although the p-sideelectrode layer 16 is represented by the thin film made from, forexample, aluminum or silver, the present invention is not limitedthereto but may be configured such that a metal layer made from gold orplatinum be stacked on the thin film made from, for example, aluminum orsilver. The thickness of each of the contact metal layer 15 and theelectrode layer 16 according to this embodiment may be changed dependingon the characteristic of light emitted by the active layer.

The contact metal layer 15 and the electrode layer 16 can be each formedby a vapor-deposition process or a plating process. At this time, thethickness or the like thereof can be changed as needed. When light aselectromagnetic waves having energy is reflected from a metal surface,the light permeates in the metal surface by a length called “penetrationdepth”. Such penetrating light is called “evanescent waves”. The lightcomponent having an energy corresponding to the complex refractive indexand the incident angle of the metal is absorbed in the metal in the formof the evanescent waves, and the light component having the remainingenergy is reflected outwardly from the metal. On the other hand, even ifthe thickness of the contact metal layer 15 is significantly thin, thecontact metal layer 15 sufficiently allows ohmic contact between theelectrode layer 16 to the GaN layer 14, and according to thisembodiment, the thickness of the contact metal layer 15 made from nickelis set to be equal to or less than the penetration depth of lightemitted by the active layer 12. As a result, it is possible to enhancethe reflecting efficiency of the electrode 10.

The current block layer 11 is formed on the tilt crystal planes so as tocover the electrodes 10, the region from the upper ends of theelectrodes 10 to the vertex portion containing the vertex of the device,and the vicinity of the bottom surface. The current block layer 11functions to suppress injection of a current into a poor crystallineregion. The current block layer 11 is formed by forming an insulatingfilm made from SiO₂ or the like, and removing a portion, correspondingto the vicinity of the bottom surface, of the insulating film byetching. The current block layer 11 is not necessarily formed by aninsulating material but may be made from a material which forms apotential barrier against the surface of a crystal layer forming thesecond cladding layer as the second conductive type semiconductor layer14 and which is less subjected to injection of a current. For example,the current block layer 11 may be configured as a thin film made from ametal material reflecting light such as Ag or Al. In the case of using amaterial reflecting light, a light reflection film can be formed on aregion in which a current is not injected, with a result that the lightemergence efficiency can be enhanced as compared with the case ofreflecting light only by the electrodes 10.

Embodiment 2

FIG. 4 is a sectional view showing the structure of a semiconductorlight emitting device according to a second embodiment of the presentinvention, which device is formed by crystal growth into anapproximately hexagonal pyramid shape having tilt crystal planes,wherein electrodes are formed on halfway areas of the tilt crystalplanes. As shown in the figure, electrodes 20 for efficient emergence oflight emitted by an input current to the outside of the device areformed, and a current block layer is formed on the electrodes 20, theupper sides of the electrodes 20, and the region in the vicinity of thevertex of the device. The current block layer has a multi-layerstructure formed by stacking a metal thin film layer 22 on an insulatinglayer 21.

The electrode 20 is formed by forming a contact metal layer 15 having athickness equal to or less than a penetration depth of light emitted byan active layer 12 formed on a crystal layer under the electrode 20, andforming an electrode layer 16 on the contact metal layer 15 having thespecific thickness. Since the thickness of the contact metal layer 15 isas thin as being equal to or less than the penetration depth of lightemitted by the active layer 12, the contact metal layer 15 can increasethe reflectance of the electrode layer 16 while allowing good ohmiccontact between the electrode layer 16 and the crystal layer. This iseffective to increase the intensity of light reflected from theelectrode layer 16 to the light transmission type substrate side. Sincethe electrode layer 16 is formed on the second conductive typesemiconductor layer 14, light traveling to the second conductive typesemiconductor layer 14 side is reflected to the substrate side. Inaddition, since the contact metal layer 15 is formed between theelectrode layer 16 and the second conductive type semiconductor layer14, it is possible to enhance the luminous efficiency as a whole.

The contact metal layer 15 allowing ohmic contact between the p-sideelectrode 20 and the second conductive type semiconductor layer 14composed of the GaN layer is made from nickel. The thickness of thecontact metal layer 15 made from nickel is set to be equal to or lessthan the penetration depth of light emitted by the active layer, andaccording to this embodiment, it is set to about 10 nm. The electrodelayer 16 is formed on the contact metal layer 15 made from nickel. Theelectrode layer 16 is represented by a thin film made from, for example,aluminum or silver. Light passing through the contact metal layer 15made from nickel is reflected from the interface of the electrode layer16. Although the electrode layer 16 is represented by the thin film madefrom, for example, aluminum or silver, the present invention is notlimited thereto but may be configured such that a metal layer made fromgold or platinum be stacked on the thin film made from, for example,aluminum or silver. The thickness of each of the contact metal layer 15and the electrode layer 16 according to this embodiment may be changeddepending on the characteristic of light emitted by the active layer.

The current block layer is formed on the tilt crystal planes so as tocover the p-side electrodes 20, the upper sides of the p-side electrodes20, and the region in the vicinity of the vertex of the device. Thecurrent block layer, which is composed of the stack of the insulatinglayer 21 and the metal thin film layer 22, functions to efficientlyreflect light emitted by the active layer 12, and hence to enhance thelight emergence efficiency. At this time, since the insulating layer 21is formed as the first layer, any current is little injected in a poorcrystalline region. As a result, it is possible to inject a current onlyin a good crystalline region under the electrodes 20. The insulatinglayer 21 may be made from an insulating material having lightpermeability. For example, the insulating layer 21 may be configured asa film-like layer made from a transparent insulating material such asSiO₂. The metal thin film layer 22 formed on the insulating layer 21 maybe configured as a film-like layer made from a metal having a highreflectance such as Ag or Al.

Embodiment 3

FIG. 5 is a sectional view showing the structure of a third embodiment,wherein electrodes are formed on halfway areas of tilt crystal planes ofan approximately hexagonal pyramid shape formed by crystal growth. Asshown in the figure, electrodes for efficient emergence of light emittedby an input current to the outside of the device are formed, and acurrent block layer having a multi-layer structure of an insulatinglayer and a metal thin film is formed to cover a region, correspondingto the upper halves of the electrodes, of the tilt crystal planes and tocover the region in the vicinity of the vertex of the device.

After an insulating layer 26 is formed in the vicinity of the vertex ofthe device, p-side electrodes 25 are formed on the insulating layer 26.In this case, the p-side electrodes 25 are formed not only to cover theinsulating layer 26 but also to cover a region, on the lower side fromthe insulating layer 26, of the tilt crystal planes. The p-sideelectrodes 25 are thus formed on the good crystalline halfway areas ofthe tilt crystal planes. The previously formed insulating layer 26functions as a current block layer for suppressing injection of acurrent in a poor crystalline region in the vicinity of the vertex ofthe device. Accordingly, since only a good crystalline region in whichthe p-side electrodes 25 are directly coupled to a second cladding layer14 can be used as a light emitting region, it is possible to enhance theluminous efficiency of light emitted by an input current.

The lower end of the insulating layer 26 on each tilt crystal plane islocated nearly at a boundary between a good crystalline region of thetilt crystal plane and a poor crystalline region which is close to thevertex of the device and which has a stepped surface and is therebypoorer in crystallinity than the halfway area of the tilt crystal plane.The lower end of the p-side electrode 25 on each tilt crystal plane islocated nearly at a boundary between a good crystalline region of thetilt crystal plane and a poor crystalline region which is close to thebottom surface of the device and which has a stepped surface and isthereby poorer in crystallinity than the halfway area of the tiltcrystal plane. The lower end of the insulating layer 26, that is, theupper end of the region in which the p-side electrode 25 is coupled withthe second cladding layer 14, and the lower end of the p-side electrode25 are set to positions where light emitted by the active layer 12 isefficiently, totally reflected from a plane portion, at which the lowerhalf of the p-side electrode 25 is not formed, of the tilt crystalplane.

The insulating layer 26 may be made from an insulating material havinglight permeability, for example, a transparent insulating material suchas SiO₂. The p-side electrode 25 is composed of a contact metal layer 15and an electrode layer 16. The contact metal layer 15 made from nickel,which is adapted to allow ohmic contact between the electrode layer 16and the GaN layer 14 is formed as a first layer. The thickness of thecontact metal layer 15 made from nickel is set to be equal to or lessthan a penetration depth of light emitted by the active layer, andaccording to this embodiment, it is set to about 10 nm. The p-sideelectrode is represented by a thin film made from aluminum or silver.Light passing through the nickel layer as the contact metal layer 15 isreflected by the interface of the electrode layer 16. Although theelectrode layer 16 is represented by the thin film made from aluminum orsilver, the present invention is not limited thereto but may beconfigured such that the a metal layer made from gold or platinum bestacked on the thin film made from aluminum or silver. In addition, thematerial of the contact metal layer 15 is not limited to nickel but maybe Pd, Co, Sb, or an alloy thereof. Since the p-side electrode 25 isformed on the insulating layer 26 having light permeability, a lightcomponent of light emitted by the active layer 12, which passes throughthe insulating layer 26 and reaches the p-side electrode 25 on theinsulating layer 26 can be efficiently reflected from the electrodelayer 26, to enhance the light emergence efficiency. In this embodiment,the electrodes 25 are formed on the halfway areas of the tilt crystalplanes of an approximately hexagonal pyramid shape; however, the presentinvention can be applied to a light emitting device having a shapedifferent from an approximately hexagonal pyramid shape insofar as ithas tilt crystal planes. Even in this case, the luminous efficiency ofthe light emitting device can be enhanced by forming the electrodes 25on halfway areas of the tilt crystal planes of the device. For example,the present invention can be applied to a light emitting device havingan approximately hexagonal truncated pyramid shape.

The present invention can be applied to a semiconductor laser other thana light emitting diode and another semiconductor light emitting device.The emission wavelength of the semiconductor light emitting device ofthe present invention is not particularly limited; however, in the caseof a device allowing emission of blue light, the p-side electrode layer16 may be made from Ag or Al.

Embodiment 4

An image display system or an illuminating system according to thepresent invention will be described below, wherein each system includesan array of a plurality of semiconductor light emitting devices each ofwhich has an electrode formed on halfway areas of tilt crystal planes ofan approximately hexagonal pyramid shape. According to this imagedisplay system and illuminating system, since the semiconductor lightemitting devices each of which exhibits a high light emergenceefficiency of light emitted by an input current, which are described ineach of the first, second, and third embodiments, are arrayed so as tobe scannable, it is possible to suppress electrode areas by using theS-planes, and hence to reduce the total area of light emitting portionsand improve the current-light conversion efficiency. In this embodiment,description will be made of a method of fabricating an image displaysystem including an array of semiconductor light emitting devices eachof which has the electrode structure described in the third embodiment.

The structure of the light emitting device will be first described.FIGS. 6A and 6B are a sectional view and a plan view of the device,respectively. A hexagonal pyramid shaped GaN layer 32 is formed byselective growth on an underlying growth layer 31 composed of a GaNbased semiconductor layer. While not shown, an insulating film is formedon the underlying growth layer 31, and the hexagonal pyramid shaped GaNlayer 32 is formed by selective growth from an opening portion formed inthe insulating film by an MOCVD process or the like. The GaN layer 32becomes a pyramid shaped growth layer covered with S-planes [(1-101)planes] when the C-plane of sapphire is used as the principal plane of asapphire substrate at the time of crystal growth. The GaN layer 32 is aregion doped with silicon. An InGaN layer 33 as an active layer isformed so as to cover the tilt S-planes of the GaN layer 32, and a GaNlayer 34 doped with magnesium is formed on the InGaN layer 33. The GaNlayer 34 doped with magnesium functions as a cladding layer.

The light emitting diode is provided with a p-electrode 35 and ann-electrode 36. The p-side electrode 35 is formed by vapor-depositing ametal material such as Ni/Pt/Au or Ni(Pd)/Pt/Au on the GaN layer 34doped with magnesium. Before the p-electrode 35 is formed, an insulatinglayer 30 having light permeability is formed in the vicinity of thevertex of the device. The insulating layer 30 can be made from atransparent insulating material such as SiO₂. The p-side electrode 35 isformed at a position determined by an angle (2θ−90°) with respect to thebottom surface. Light emitted by the active layer under the p-sideelectrode 35 is efficiently, totally reflected from the p-side electrode35 and the tilt crystal planes, to emerge to the outside of the device.The n-electrode 36 is formed in an opening portion formed in theabove-described insulating film (not shown) by vapor-depositing a metalmaterial such as Ti/Al/Pt/Au. In this embodiment, if the n-electrode isformed at a portion, apart from the light emergence surface, of the backsurface of the underlying growth layer 31, it is not required to formthe n-electrode 36 on the front surface of the underlying growth layer31.

The GaN based light emitting device having such a structure allowsemission of even blue light. In particular, such a light emitting devicecan be relatively simply peeled from the sapphire substrate by laserabrasion. In other words, each device can be selectively peeled byselectively irradiating the device with laser beams. In the lightemitting diode according to this embodiment, light emitted by the activelayer passes through the GaN layer and emerges out from the bottom sidethrough the underlying growth layer 31, or efficiently, totallyreflected from the p-side electrode 35 or the tilt crystal planes, andthen passes through the GaN layer 32 and emerges out from the bottomside through the underlying growth layer 31. The GaN based lightemitting device may have a structure including the active layer formedinto a planar or strip shape, or a pyramid structure including theC-plane formed at the upper end portion of the pyramid. In addition, theGaN light emitting diode may be replaced with any other nitride basedlight emitting device or a compound semiconductor device.

The step of peeling light emitting devices from the substrate on whichthe devices remain as having been formed, and covering each of thedevices with a resin layer will be described below. As shown in FIG. 7,a plurality of light emitting diodes 42 are formed in a matrix patternon the principal plane of a first substrate 41. The size of the lightemitting devices 42 is set to about 20 μm. The first substrate 41 is asubstrate for growing a crystal layer constituting the light emittingdiode 42. The material of the first substrate 41 is not particularlylimited insofar as a crystal layer having tilt crystal planes can beformed on the substrate. The first substrate 41 used in this embodimentis a sapphire substrate made from a material having high lightpermeability against a wavelength of a laser beam used for irradiationof the light emitting diode 42. The first substrate 41 uses the C-planeof sapphire as the principal plane which has been often used for growinga gallium nitride (GaN) based compound semiconductor material. It is tobe noted that the term “C-plane” used herein is not limited to thestrict C-plane but may include a plane tilted therefrom by an angleranging from 5 to 6°. The light emitting diode 42 is already providedwith a p-electrode and the like but is not subjected to final wiring.Grooves 42 g for device isolation are formed so as to individuallyisolate the light emitting diodes 42 from each other. The grooves 42 gare formed, for example, by reactive ion etching. Such a first substrate41 is opposed to a temporarily holding member 43 for selective transferof the light emitting diodes 42 therebetween.

Both a peelable layer 44 and an adhesive layer 45 are formed on thesurface, opposed to the first substrate 41, of the temporarily holdingmember 43. Here, a glass substrate or a quartz glass substrate can beused as the temporarily holding member 43. The peelable layer 44 on thetemporarily holding member 43 may be made from a material such as afluorocarbon resin, a silicone resin, a water-soluble adhesive (forexample, polyvinyl alcohol: PVA), or polyimide. As one example, apolyimide film as the peelable layer 44 is formed on a quartz glasssubstrate as the temporarily holding member 43 to a thickness of about 1μm to 3 μm, and a UV-curing type adhesive layer as the adhesive layer 45is formed on the peelable layer 44 to a thickness of about 20 μm.

The adhesive layer 45 of the temporarily holding member 43 is adjustedto be divided into cured regions 45 s and non-cured regions 45 y. Thefirst substrate 41 is aligned to the temporarily holding member 43 insuch a manner that each of the light emitting devices 42 to beselectively transferred to the temporarily holding member 43 ispositioned at the non-cured region 45 y. The adjustment of the adhesivelayer 45 such that the adhesive layer 45 is divided into the curedregions 45 s and the non-cured regions 45 y may be performed byselectively exposing the adhesive layer 45 (made from the UV-curing typeadhesive) with a pitch of 200 μm, thereby forming the cured regions 45 sand the non-cured regions 45 y (to which the light emitting devices 42are to be transferred) arranged with a pitch of 200 μm. After suchalignment, the light emitting diode 42 to be transferred is peeled fromthe first substrate 41 by making use of laser abrasion. Since the GaNbased light emitting diode 42 is decomposed into Ga (metal) and nitrogenat the interface with sapphire, it can be easily peeled from the firstsubstrate 41. The laser beam used herein may be an excimer laser beam ora harmonic YAG laser beam.

The light emitting diode 42, which has been selectively irradiated withlaser beams, is peeled from the first substrate 41 at the boundarybetween the GaN layer and the first substrate 41 by laser abrasion, andis transferred to the opposed temporarily holding member 43 in such amanner that the p-electrode of the light emitting diode 42 is pierced inthe adhesive layer 45 of the temporarily holding member 43. The otherlight emitting diodes 42, which are not irradiated with laser beams andare positioned at the cured regions 45 s of the adhesive layer 45, arenot transferred to the temporarily holding member 43 side. In theexample shown in FIG. 7, only one light emitting diode 42 is selectivelyirradiated with laser beams; however, in actual, the light emittingdiodes 42 spaced from each other with a pitch “n” are irradiated withlaser beams. With such selective transfer, the light emitting diodes 42are re-arrayed on the temporarily holding member 43 with a pitch largerthan the array pitch of the light emitting diodes 42 on the firstsubstrate 41.

The light emitting diode 42 is held by the adhesive layer 45 of thetemporarily holding member 43 with the back surface of the lightemitting diode 42 taken as the n-electrode (cathode electrode) side, andsince the resin (adhesive) is removed from the back surface of the lightemitting diode 42 by cleaning, an electrode pad 46 can be formed on theback surface of the light emitting diode 42 as shown in FIG. 8 in such amanner as to be electrically connected thereto.

As one example of cleaning of the adhesive layer 45, the resin(adhesive) of the adhesive layer 45 is etched with oxygen plasma andthen cleaned by irradiation of UV ozone. In addition, when the GaN basedlight emitting diode is peeled from the first substrate 41 made fromsapphire by laser abrasion, Ga is deposited on the peeled plane.Accordingly, such an element Ga must be etched with a NaOH containingwater solution or dilute nitric acid. After that, the electrode pad 46is patterned. At this time, the electrode pad on the cathode side can beformed into a size of about 60 μm square. As the electrode pad 46, therecan be used a transparent electrode (ITO or ZnO based electrode) or anelectrode made from a material such as Al/Cu. In the case of using atransparent electrode, even if the electrode largely covers the backsurface of the light emitting diode, it does not shield light emission.As a result, a patterning accuracy of the electrode can be roughened andthe size of the electrode can be made large. This is advantageous infacilitating the patterning process.

The step of transferring each light emitting diode 42 from the firsttemporarily holding member 43 to a second temporarily holding member 47will be described below. A peelable layer 48, a light emitting diode 42to be transferred, and a peelable layer 48 are formed on the secondtemporarily member 47 to which the light emitting diode 42 is to betransferred. The peelable layer 48 can be made from a resin having lightpermeability such as a fluorocarbon resin, a silicone resin, awater-soluble adhesive (for example, PVA), or polyimide. As one example,a glass substrate is used as the second temporarily holding member 47.

The temporarily holding member 43 is opposed to the temporarily holdingmember 47 provided with the peelable layer 48 in such a manner that theadhesive layer 45 is brought into close-contact with the peelable layer48. In such a state, to separate the peelable layer 44 from thetemporarily holding member 43, the temporarily holding member 43 isirradiated with excimer laser beams from the side, opposed to thesurface provided with the peelable layer 44, of the temporarily holdingmember 43. At this time, the temporarily holding member 43 is irradiatedwith excimer laser beams from the back surface, opposed to the surfaceprovided with the peelable layer 44, of the temporarily holding member43. Since the temporarily holding member 43 is made from glass, theexcimer laser beams is little absorbed in the temporarily holding member43, to irradiate the vicinity of the interface between the peelablelayer 44 and the temporarily holding member 43, thereby causing laserabrasion thereat. As a result, the adhesive force between the peelablelayer 44 and the temporarily holding member 43 is lowered, and therebyonly the temporarily holding member 43 is separated from the devicestructure including each light emitting diode 42 and the peelable layer44 as the uppermost layer. Each light emitting diode 42 is thustransferred to the second temporarily holding member 47 side.

At this time, since the peelable layer 44 have a sufficient filmthickness, it absorbs all of the excimer laser beams having passedthrough the temporarily holding member 44. Accordingly, the excimerlaser beams do not reach the layers under the peelable layer 44. Inother words, the adhesive layer 45 and the peelable layer 48 are notdeteriorated by the excimer laser beams.

FIG. 9 shows a dicing state of the adhesive layer 45. After the lightemitting diode 42 is transferred from the temporarily holding member 43to the second temporarily holding member 47, a via-hole 50 on the anodeelectrode (p-electrode) side is formed and an anode side electrode pad49 is formed. Thereafter, the adhesive layer 45 made from the resin isdiced. As a result of dicing, device isolation grooves 51 are formed, toisolate each light emitting diode 42 from those adjacent thereto,whereby each resin-molded device having a specific shape is formed. Theresin-molded device is in the state being adhesively bonded on thetemporarily holding member 47. To isolate the light emitting diodes 42arrayed in a matrix from each other, the device isolation grooves 51have a planar pattern composed of a plurality of parallel linesextending in the vertical and horizontal directions. The bottom of thedevice isolation groove 51 faces to the surface of the secondtemporarily holding member 47.

The step of forming the anode side electrode pad 49 of each lightemitting diode 42 and then forming the device isolation grooves 51 willbe more fully described below. In one example of such a process, thesurface of the second temporarily holding member 47 is etched withoxygen plasma until the surface of the light emitting diode 42 isexposed. The via-hole 50 is formed by using excimer laser beams,harmonic YAG laser beams, or carbon dioxide laser beams. At this time,the diameter of the via-hole is set to about 3 to 7 μm. The anode sideelectrode is made from Ni/Pt/Au. The dicing process may be performed byusing a general blade, and if a narrow cut-in width of 20 μm or less isrequired, the dicing process may be performed by laser cutting. As thelaser beams used for cutting, there may be used excimer laser beams,harmonic YAG laser beams, or carbon dioxide laser beams. The cut-inwidth is dependent on the size of the light emitting diode covered withthe adhesive layer 45 made from the resin to be located in a pixel of animage display unit. As one example, grooves each having a width of about40 μm are formed by excimer laser beams, to divide the device structureinto the individual devices, thereby forming the resin-molded deviceseach having a specific shape.

The step of peeling each resin-molded device containing the lightemitting device 42 from the second temporarily holding member 47 andsimultaneously forming irregularities on the peelable layer 48 will bedescribed below. First, as shown in FIG. 10, the resin-molded device ispeeled from the second temporarily holding member 47 and is then alignedto an attraction hole 55 for transfer. In actual, a number of theattraction holes 55 arrayed in a matrix with a pitch corresponding to apixel pitch of an image display unit are formed in order to collectivelyattract a number of the resin-molded devices. To be more specific, theattraction holes 55, each having an opening diameter of about 100 μm,are arranged with a pitch of 600 μm in order to collectively attract theresin-molded devices of the number of about 300 pieces. The attractionholes 55 may be formed by preparing a metal plate 52 made from Ni byelectrocasting or a stainless steel and forming holes in the metal plate52 by etching.

The vicinity of the interface between each resin-molded device alignedto the corresponding attraction hole 55 and the second temporarilyholding member 47 is irradiated with energy beams. The energy beams areemitted from the side, opposed to the surface on which the resin-moldeddevice remains as adhesively bonded, of the second temporarily holdingmember 47. Since the second temporarily holding member 47 is made fromglass having light permeability, the energy beams are little absorbed inthe second temporarily holding member 47. As a result, the peelablelayer 48, located in the vicinity of the interface of the holding member47, of the resin-molded device is irradiated with the energy beams. Thepeelable layer 48 irradiated with the energy beams loses the adhesiveforce for adhesively bonding the temporarily holding member 47 by laserabrasion. According to this embodiment, excimer laser beams are used asthe energy beams; however, other laser beams such as YAG laser beams maybe used as the energy beams.

In the state that the adhesive force between the resin-molded device andthe holding member 47 is lowered, the pressure of an attracting chamber54 communicated to the attraction hole 55 is controlled to a negativepressure, to allow attraction of the light emitting diode 42 in the formof the resin-molded device. The light emitting diode 42 in the form ofthe resin-molded device is thus peeled from the second temporarilyholding member 47 by using a mechanical means.

FIG. 11 is a view showing the transfer of each resin-molded device to asecond substrate 60 which is part of an image display system. The secondsubstrate is made from a material having light permeability such asglass. At the time of mounting each resin-molded device to the secondsubstrate 60, an adhesive layer 56 is previously formed on the secondsubstrate 60. A region, to which each light emitting diode 42 in theform of the resin-molded device is mounted, of the adhesive layer 56 iscured, so that each light emitting diode 42 is fixedly arrayed on thesecond substrate 60. At the mounting of each light emitting diode 42,the pressure of the attracting chuck 54 of an attracting device 53 iscontrolled to a positive pressure in order to apply a force to theresin-molded device in the direction where the resin-molded device isremoved from the attraction hole 55. In other words, at this time, theattraction state between the attracting device 53 and the light emittingdevice 42 is released. The adhesive layer 56 is made from athermosetting adhesive or a thermoplastic adhesive. The light emittingdiodes 42 in the form of the resin-molded diodes are arrayed on thesecond substrate 60 in such a manner as to be spaced from each otherwith a pitch larger than each of the pitch of the diodes on thetemporarily holding member 43 and the pitch of the diodes on thetemporarily holding member 47. It is to be noted that the energy beams(laser beams 73) for curing the resin of the adhesive layer 56 issupplied from the back surface of the second substrate 60.

Only a portion, corresponding to the resin-molded device (light emittingdiode 42 and the adhesive layer 45) to be transferred, of the adhesivelayer 56 is irradiated with the laser beams 73 from the back surface ofthe second substrate 60, to be thus heated. With such heating of theadhesive layer 56, if the adhesive layer 56 is made from a thermoplasticresin, the heated portion of the adhesive layer 56 is softened, to becooled and cured, whereby the resin-molded chip being in contact withthe cured portion of the adhesive layer 56 is fixed to the secondsubstrate 60. Similarly, if the adhesive layer 56 is made from athermosetting adhesive, only a portion, irradiated with the laser beams73, of the adhesive layer 56 is cured, whereby the resin-molded chipbeing in contact with the cured portion of the adhesive layer 56 isfixed to the second substrate 60.

An electrode layer 57, which also functions as a shadow mask, isdisposed on the second substrate 60. The electrode layer 57 may beirradiated with the laser beams 73, to be heated, thereby indirectlyheating the adhesive layer 56. In particular, a black chromium layer 58may be formed on the surface, on the screen side, that is, the viewerside, of the electrode layer 57. This is advantageous in improving thecontrast of an image, and further increasing the energy absorption rateof the black chromium layer 58, thereby efficiently heating the adhesivelayer 56 by selectively irradiating the black chromium layer 58 with thelaser beams 73.

FIG. 12 is a view showing a state that the resin-molded devicescontaining the light emitting diodes denoted by references 42, 61, and62 are arrayed on the second substrate 60 and are covered with aninsulating layer 59. The resin-molded devices 42, 61 and 62 can bemounted at desired positions by using the attracting device 53 shown inFIG. 10 or 11. In this case, the process of mounting each of theresin-molded devices 42, 61 and 62 may be performed in the same manneras that described above except that the position, at which thecorresponding device 42, 61 or 62 is to be mounted, of the secondsubstrate 60 is suitably shifted. The insulating layer 59 may be madefrom a transparent epoxy adhesive, a UV-curing type adhesive, orpolyimide.

FIG. 13 is a view showing a wiring step for forming opening portions 65,66, 67, 68, 69, and 70 in the insulating layer 59, and also formingwiring lines 63, 64, and 71 for connecting the anode and cathodeelectrode pads of the light emitting diodes 42, 61, and 62 to theelectrode layer 57 (wiring electrode) formed on the second substrate 60.Since the areas of the electrode pads 46 and 49 of each of the lightemitting diodes 42, 61 and 62 are large, the shapes of the openingportions, that is, the via-holes can be made large, with a result thatthe positioning accuracy of each via-hole may be rough as compared witha via-hole directly formed in each light emitting diode. To be morespecific, when each of the electrode pads 46 and 49 having a size ofabout 60 μm square is provided, the via-hole having a diameter of about20 μm can be formed. Since the via-holes are of three kinds connected tothe wiring substrate, the anode electrode, and the cathode electrode,the depth of each via-hole may be optimized by controlling the pulsenumber of laser beams depending on the kind of the-via-hole. Aprotective layer is then formed on the wiring lines, to accomplish apanel of an image display system. The protective layer may be made fromthe same transparent epoxy adhesive as that used for the insulatinglayer. The protective layer is cured by heating, to perfectly cover thewiring lines. After that, a driver IC is connected to the wiring at theend portion of the panel, to fabricate a drive panel. An image displaysystem capable of creating a high quality image, which includes an arrayof the devices each exhibiting a high light emergence efficiency by acurrent inputted in the device, can be accomplished by theabove-described production steps.

INDUSTRIAL APPLICABILITY

As described above, according to the semiconductor light emitting deviceand a fabrication method thereof according to the present invention, itis possible to provide a semiconductor light emitting device capable ofexhibiting both a high light emergence efficiency and a high luminousefficiency. According to the image display system and the illuminatingsystem, each of which includes an array of the semiconductor lightemitting devices of the present invention, and fabrication methodsthereof according to the present invention, it is possible to provide animage display system capable of reducing the density of a currentinjected to each device and also displaying a high quality image, andalso to provide an illuminating system capable of increasing brightness.In particular, the image display system and illuminating system, each ofwhich includes the array of a large number of light emitting devices,are advantageous in reducing power consumption.

1. A semiconductor light emitting device comprising: a crystal layercomprising: a first conductive type layer, an active layer, and a secondconductive type layer formed on a crystal growth layer, wherein thesecond conductive type is different from the first conductive type andthe active layer is between the first conductive type layer and thesecond conductive type layer; wherein the crystal layer has anapproximately hexagonal pyramid shape comprising a plurality of tiltcrystal planes that are tilted from a principal plane of a substrate andthat intersect at a vertex of the approximately hexagonal pyramid shape,and wherein the first conductive type layer, the active layer, and thesecond conductive extend within planes parallel to the tilt crystalplanes; an electrode formed on only a partial area of a first tiltcrystal plane of the plurality of tilt crystal planes; wherein saidelectrode is formed in a region on the first tilt crystal plane havingbetter crystallinity as compared to both a region of said first tiltcrystal plane in the vicinity of the vertex and a region of said firsttilt crystal plane in the vicinity of a bottom surface of the device;and wherein the light emitting device is constructed such that at leastsome light generated by the crystal layer is reflected by a surface ofthe tilt crystal planes and emerges from the device through a lightemergence plane on the bottom surface of the device.
 2. A semiconductorlight emitting device as claimed in claim 1, wherein an angle formedbetween the principal plane of said substrate and the first tilt crystalplane is taken as θ, a first ridge line adjacent said first tilt crystalplane tilted from the principal plane of said substrate by an angle ofθ, the first plane containing a first point on the first ridge lineadjacent said first tilt crystal plane, the second plane containing asecond point on the first ridge line adjacent said first tilt crystalplane, the first point on the first ridge line is defined by a point atwhich a first straight line tilted from a bottom side of an opposingtilt crystal plane by an angle of 2θ−90° intersects the first ridgeline, the second point on the first ridge line is defined by a point atwhich a second straight line tilted from the first plane by an angle of2θ−90° intersects the first ridge line, said opposing tilt crystal planeforming an angle of θ with the principal plane of said substrate, asecond ridge line adjacent said opposing tilt crystal plane tilted fromthe principal plane of said substrate by an angle of θ, the firststraight line starting from an intersection between the bottom side ofsaid opposing tilt crystal plane and the second ridge line, and thesecond straight line starting from an intersection between the firstplane and the second ridge line.
 3. A semiconductor light emittingdevice according to claim 1, wherein said electrode is a p-sideelectrode.
 4. A semiconductor light emitting device according to claim1, wherein an insulating layer is formed on the tilt crystal planes. 5.A semiconductor light emitting device according to claim 4, wherein saidinsulating layer is formed in the vicinity of the vertex.
 6. Asemiconductor light emitting device according to claim 5, wherein saidinsulating layer is formed away from the vicinity of a bottom surface ofsaid semiconductor light emitting device.
 7. A semiconductor lightemitting device according to claim 6, wherein said vertex is bounded bysaid insulating layer.
 8. A semiconductor light emitting deviceaccording to claim 1, wherein said crystal growth layer has a wurtzitetype crystal structure.
 9. A semiconductor light emitting deviceaccording to claim 1, wherein said crystal growth layer is made from anitride semiconductor.
 10. A semiconductor light emitting deviceaccording to claim 1, wherein said crystal layer is provided byselective growth on said substrate via an underlying growth layer.
 11. Asemiconductor light emitting device according to claim 10, wherein saidselective growth is performed by making use of selective removal of saidunderlying growth layer.
 12. A semiconductor light emitting deviceaccording to claim 11, wherein said selective growth is performed bymaking use of an opening portion selectively formed in a mask layer. 13.A semiconductor light emitting device according to claim 12, whereinsaid crystal layer is formed by selective growth from said openingportion formed in said mask layer in such a manner as to be spread fromsaid opening portion in a lateral direction.
 14. A semiconductor lightemitting device according to claim 1, wherein the principal plane ofsaid substrate is approximately a C-plane.
 15. A semiconductor lightemitting device according to claim 1, wherein the tilt crystal planecontains at least one of an S-plane and an (11-22) plane.
 16. Asemiconductor light emitting device according to claim 1, wherein acurrent from the electrode is mainly injected into the first tiltcrystal plane.
 17. A semiconductor light emitting device according toclaim 1, wherein said active layer is made from InGaN.
 18. Asemiconductor light emitting device according to claim 1, wherein saidtilt crystal planes are symmetrically disposed.
 19. A semiconductorlight emitting device as claimed in claim 1, further comprising a lightreflection film formed on the tilt crystal planes so as to cover aregion comprising the vertex, wherein said light reflection film isadapted to reflect light emitted by the active layer.
 20. An imagedisplay system comprising an array of semiconductor light emittingdevices for emitting light in response to signals, said semiconductorlight emitting devices being each formed by forming a crystal layerhaving an approximately hexagonal pyramid shape comprising a pluralityof tilt crystal planes that are tilted from a principal plane of asubstrate and that intersect at a vertex of the approximately hexagonalpyramid shape, wherein the crystal layer comprises a first conductivetype layer, an active layer, and a second conductive type layer, whereinthe second conductive type is different from the first conductive typeand the active layer is between the first conductive type layer and thesecond conductive type layer, and wherein said crystal layer is formedin such a manner that said first conductive type layer, said activelayer, and said second conductive type layer extend within planesparallel to the tilt crystal planes, and wherein an electrode is formedon only a partial area of a first tilt crystal plane of the plurality oftilt crystal planes; wherein said electrode is formed in a region on thefirst tilt crystal plane having better crystallinity as compared to botha region of said first tilt crystal plane in the vicinity of the vertexand a region of said first tilt crystal plane in the vicinity of abottom surface of the device; and wherein each light emitting device isconstructed such that at least some light generated by the crystal layeris reflected by a surface of the tilt crystal planes and emerges fromthe device through a light emergence plane on the bottom surface of thedevice.
 21. An image display system as claimed in claim 20, wherein anangle formed between the principal plane of said substrate and the firsttilt crystal plane is taken as θ, a first ridge line adjacent said firsttilt crystal plane tilted from the principal plane of said substrate byan angle of θ, the first plane containing a first point on the firstridge line adjacent said first tilt crystal plane, the second planecontaining a second point on the first ridge line adjacent said firsttilt crystal plane, the first point on the first ridge line is definedby a point at which a first straight line tilted from a bottom side ofan opposing tilt crystal plane by an angle of 2θ−90° intersects thefirst ridge line, the second point on the first ridge line is defined bya point at which a second straight line tilted from the first plane byan angle of 2θ−90° intersects the first ridge line, said opposing tiltcrystal plane forming an angle of θ with the principal plane of saidsubstrate, a second ridge line adjacent said opposing tilt crystal planetilted from the principal plane of said substrate by an angle of θ, thefirst straight line starting from an intersection between the bottomside of said opposing tilt crystal plane and the second ridge line, andthe second straight line starting from an intersection between the firstplane and the second ridge line.
 22. An image display system accordingto claim 20, wherein said electrode is a p-side electrode.
 23. An imagedisplay system as claimed in claim 20, further comprising a lightreflection film formed on the tilt crystal planes so as to cover aregion comprising the vertex, wherein said light reflection film isadapted to reflect light emitted by the active layer.
 24. Anilluminating system comprising an array of semiconductor light emittingdevices for emitting light in response to signals, said semiconductorlight emitting devices being each formed by forming a crystal layerhaving an approximately hexagonal pyramid shape comprising a pluralityof tilt crystal planes that are tilted from a principal plane of asubstrate and that intersect at a vertex at the top of the approximatelyhexagonal pyramid shape, wherein the crystal layer comprises a firstconductive type layer, an active layer, and a second conductive typelayer, wherein the second conductive type is different from the firstconductive type and the active layer is between the first conductivetype layer and the second conductive type layer, and wherein saidcrystal layer is formed in such a manner that said first conductive typelayer, said active layer, and said second conductive type layer extendwithin planes parallel to the tilt crystal planes, and wherein anelectrode is formed on only a partial area of a first tilt crystal planeof the plurality of tilt crystal planes; wherein said electrode isformed in a region on the first tilt crystal plane having bettercrystallinity as compared to both a region of said first tilt crystalplane in the vicinity of the vertex and a region of said first tiltcrystal plane in the vicinity of a bottom surface of the device; andwherein each light emitting device is constructed such that at leastsome light generated by the crystal layer is reflected by a surface ofthe tilt crystal planes and emerges from the device through a lightemergence plane on the bottom surface of the device.
 25. An illuminatingsystem as claimed in claim 24, wherein an angle formed between theprincipal plane of said substrate and the first tilt crystal plane istaken as θ, a first ridge line adjacent said first tilt crystal planetilted from the principal plane of said substrate by an angle of θ, thefirst plane containing a first point on the first ridge line adjacentsaid first tilt crystal plane, the second plane containing a secondpoint on the first ridge line adjacent said first tilt crystal plane,the first point on the first ridge line is defined by a point at which afirst straight line tilted from a bottom side of an opposing tiltcrystal plane by an angle of 2θ−90° intersects the first ridge line, thesecond point on the first ridge line is defined by a point at which asecond straight line tilted from the first plane by an angle of 2θ−90°intersects the first ridge line, said opposing tilt crystal planeforming an angle of θ with the principal plane of said substrate, asecond ridge line adjacent said opposing tilt crystal plane tilted fromthe principal plane of said substrate by an angle of θ, the firststraight line starting from an intersection between the bottom side ofsaid opposing tilt crystal plane and the second ridge line, and thesecond straight line starting from an intersection between the firstplane and the second ridge line.
 26. An illuminating system according toclaim 24, wherein said electrode is a p-side electrode.
 27. Anilluminating system as claimed in claim 24, further comprising a lightreflection film formed on the tilt crystal planes so as to cover aregion comprising the vertex, wherein said light reflection film isadapted to reflect light emitted by the active layer.